<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

</body>
<!--
    1. 基本数据类型
    2. null和undefined的比较
         1. 赋值过程
         2. typeof
-->
<script>

   var num;

   console.log(num) ;
   console.log(typeof num) ;

   var num=100;
   console.log(num);

   var num=null;

   console.log(num);
   console.log(typeof num) ;

  /* console.log(typeof num);

   num='hell0';

   console.log(typeof num);

   num=false;

   console.log(typeof num);

   num={};
   console.log(typeof num);

   */

   num=null;

   console.log(typeof num);
   console.log(num instanceof Object);

   num=[];
   console.log(typeof num);
   console.log( num instanceof Array);


</script>
</html>